A conventional belt retractor comprises a frame, a belt reel rotatably mounted in the frame, a belt reel axle with an external toothing, and a pawl. Modern belt retractors are often equipped with additional functions beside the usual belt-webbing-sensitive and/or vehicle-sensitive locking functions. One of these additional functions is the precautionary tensioning of the belt webbing in a critical situation, e.g. at full braking. In modern systems, tensioning a belt webbing in the case of an impending vehicle impact can be effected by an electric motor, in particular a servomotor. When using a powerful electric motor drive, a belt slack possibly existing can already be removed with such pretensioning prior to an accident, in order to minimize the risk of injuries for the occupants. Moreover, the functioning of a belt tensioner can be improved as compared to a conventional system.
It is the object underlying the invention to provide a belt retractor in which the use of an electric motor provides for a fast and reliable tensioning of the belt.